Module 3: Transport in Plants

Question 1

Need for a transport system in plants

Answer 1

Move water from roots up to the leaves

Move sugars from leaves to rest of the plant

Question 2

Structure and function of vascular system in roots

Answer 2

Xylem in the centre often in an ‘X’ shape with phloem in between the arms of Xylem
This arrangement provides strength to withstand pulling forces

Question 3

Structure and function of vascular system in stems

Answer 3

Vascular bundle found near the outer edge of plant with xylem toward the inside, phloem towards the outside and a layer of cambium between them.
This arrangement provides strength and flexibility to withstand bending forces

Question 4

Structure and function of vascular system in leaves

Answer 4

Xylem and phloem arranged in veins with xylem toward the top and phloem toward the bottom

Question 5

Structure and function of Xylem

Answer 5

Tissue used to transport water and mineral ions from roots up to the leaves and other parts of the plant.
Consist of xylem vessels which contain lignin which strengthens the vessel walls and prevents the vessel from collapsing.

Question 6

Structure and function of Phloem

Answer 6

Tissue used to transport assimilates around the plant.
Made of sieve tube elements stacked end to end to make a narrow tube with a sieve plate between them. Sieve plates contain many pores that allow sugars through
Each phloem cell is supported by a companion cell that loads sugars into the phloem. Companion and phloem cells are linked by plasmodesmata.

Question 7

What is Transpiration?

Answer 7

Loss of water vapour from the upper parts of the plant

Question 8

Process of transpiration

Answer 8

1. Water enters the leaf through the xylem and moves by osmosis into the cells of the spongy mesophyll
2. Water evaporates from the cell walls of spongy mesophyll
3. Water vapour moves by diffusion out of the leaf through open stomata as water vapour potential is higher inside the leaf than outside

Question 9

Importance of Transpiration

Answer 9

Transports useful mineral ions up the plant
Maintains cell turgidity
Supplies water for growth, cell elongation and photosynthesis

Question 10

Factors affecting transpiration

Answer 10

+ Light intensity- In light stomata open to allow gas exchange for photosynthesis
+ Temperature- High temp. increases rate of evaporation and diffusion
- Water availability- If there is little water in soil, plant cannot replace water that is lost

Question 11

Transport of water into the plant

Answer 11

Water enters the root hair cells by osmosis. Then moves by osmosis across the cortex through the endodermis to the xylem.
Minerals are actively transported across the endodermis into the xylem lowering water potential in xylem.
3 pathways water can take
Apoplast- water passes through spaces in cell walls and between the cells
Symplast- water passes through plasmodesmata of adjacent cells
Vacuolar- water moves through vacuoles of adjacent cells

Question 12

Movement of water up the stem

Answer 12

Water moves up the xylem in a transpiration stream held together by cohesion and adhesion
This creates a tension and water is pushed up the xylem by the root pressure of water and pulled up the xylem by transpiration.

Question 13

Adaptations of plants to the availability of water in the environment (Xerophyte)

Answer 13

Conserve water by storing it in stems or leaves
Prevent water being lost by having coiled leaves , sunken stomata and small hairs around stomata to catch water droplets
This increases water vapour potential around stomata decreasing transpiration

Question 14

Adaptations of plants to the availability of water in the environment (Hydrophyte)

Answer 14

Many large air spaces in leaf to keep leaves afloat
stomata is on upper epidermis so they are exposed to air. Allows gaseous exchange from surface of the leaves and transpiration of water

Question 15

Mechanism of translocation

Answer 15

1. Active transport of H+ ions out of companion cells this creates concentration gradient
   hydrogen ions diffuse back into cell with sucrose through cotransport proteins
   assimilates diffuse through plasmodesmata from companion cell into sieve tube.
2. Water from the xylem moves into the phloem by osmosis creating high hydrostatic pressure. This pressure forces assimilates along the phloem
3. At the other end of the phloem, the components of the assimilates are actively loaded out, increasing water potential in the sieve tube. water then moves out if the sieve tube and reduces hydrostatic pressure